1. Field of the Invention
The present invention relates to a method and apparatus for producing superconductors in the form of an elongated tape.
2. Description of the Related Art
Although there is considerable technical and economic incentive to make superconducting magnets from A-15 type superconductors, especially from the so-called post-Niobium-Tin superconductors, e.g., Nb-Al, Nb-GE, Nb-Ga, this new class of superconductors have proven to be difficult to process into bundles of fine wire as had been the practice with superconducting compounds previously used, such as niobium-titanium. Further, attempts to date at making tape superconductors of the A-15 type have been successful in producing only short lengths of tape superconductors. Splicing such short lengths into longer, useful lengths of superconductor tape creates serious problems with the reliability of the conductor.
Perhaps the most common processes to date for forming A-15 type superconducting materials are plasma spray forming and the melt spinning. The former has the disadvantage that the conductors must be formed in relatively thick sections in order to ensure continuity of the superconductor material and of its superconductive properties. The melt spinning process has the disadvantage that there is a limitation on the amount of material which can be molten and ejected out under pressure to form a thin film on a substrate. The process is therefore not believed to be well suited for large scale production of superconductor products. Chemical vapor deposition (CVD) could be employed as well, but this process is slow and costly and also would not be well suited for large scale production.
Other processes disclosed in the art include forming a bulk "tape" of the superconducting material and heating and melting a center part of the tape such that the melted and resolidified section forms a compound superconductor region on the tape. The process has at least one disadvantage in that a much larger amount of the base material is required than is actually converted to the superconductive material. A further process disclosed in the art calls for forming a substrate of one of the elements of the compound superconductor and applying to the substrate a coating of a second element of the compound, heat treating the coated substrate to produce intermetallic compounds, and subsequently irradiating the coated substrate with a high-energy density beam such as an electron beam or laser beam. The process has the disadvantage that numerous process steps are required before the superconducting material is produced. Because both of these processes involve preparing a substrate for later processing, the processes will generally only be useful in producing superconductors of some finite length. Still other methods proposed in the art have similar drawbacks and provide further evidence of the difficulties in producing superconductor products using A-15 type compound superconductors.
It is therefore a principal object of the present invention to provide a simplified method for producing long lengths of superconductor tape.
It is another object of the present invention to provide a method for producing a superconductive tape of an A-15 type compound superconductor suitable for use in superconductor magnets. It is a further object of the present invention to provide a method for substantially continuous production of superconductive tape products of indeterminate length.
It is yet a further object of the present invention to provide a method for producing superconductor tape products which is especially well suited for on-line dimensional control and quality control of the tape product.
It is a further object of the present invention to provide an apparatus for producing elongated tape superconductors at speeds suitable for large scale production.